The present invention relates to clock data recovery circuitry including level shifting circuits.
Integrated circuit (“IC”) designs increasingly require interface between ICs, or between portions within a single IC, that have different voltage requirements. Level shifting circuits are used to accomplish changing a voltage level of an electronic signal from a first value to a second value.
When shifting from a signal having a smaller voltage to a signal having a higher voltage, many existing level shifting circuits rely at least in part on transistors that have threshold voltages capable of tolerating the full voltage range of the larger voltage signal. Such transistors typically have thicker insulating (e.g., oxide) layers than do transistors in circuits that process the smaller signal. Thicker oxide transistors can tolerate the voltage difference generated by the larger signal. However, use of thicker oxide devices can limit the switching speed of the circuit and hence limit the frequency of signals that the circuit is capable of generating or transmitting. There is therefore a need for level shifting circuits that can utilize transistors having thinner insulating layers to generate signals of a given voltage range.